Providing dynamic field of view for light received from a dynamic position

ABSTRACT

A system and method for providing a dynamic composite field of view in a scanning lidar system, such as to improve a signal-to-noise ration of detected light. The dynamic composite field of view can include a subset of the available detector pixels, and can thereby reduce noise introduce by noise sources that can scale with a detector area, such as dark current and gain peaking that can be caused by a capacitance of the photodetector.

CLAIM OF PRIORITY

This patent claims the benefit of priority of Provisional PatentApplication Ser. No. 62/449,716, filed Jan. 24, 2017, which is herebyincorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to systems and methods for improvingaccuracy in a system receiving light from a moving source, such as in ascanning laser range finding system or free space optical communicationsystem.

SUMMARY OF THE DISCLOSURE

Certain systems, such as lidar systems, can scan a light beam across atarget region and detect the scanned light beam reflected or scatteredby the target region. The inventors have recognized, among other things,that it is possible to provide a dynamic field of view as the light beamscans across the target region, such as can provide an improvedsignal-to-noise ratio of the detected light. Further features of thedisclosure are provided in the appended claims, which features mayoptionally be combined with each other in any permutation orcombination, unless expressly indicated otherwise elsewhere in thisdocument.

In an aspect, the disclosure can feature a method for dynamicallyadjusting a composite field of view in a lidar system having aphotosensitive detector. The method can include selecting a first groupof detector pixels, such as for detecting a portion of a light beamtransmitted towards a target region. The method can also includeadjusting an angle of the light beam transmitted towards the targetregion. The method can also include then selecting a second group ofdetector pixels, such as for detecting a portion of the light beamhaving the adjusted angle. The method can also include subtracting atleast one detector pixel from the first group of detector pixels andadding at least one detector pixel to the first group of detectorpixels, such as to form the second group of detector pixels. Thedetected light beam can include an area corresponding to M pixels andthe first group of detector pixels and the second group of detectorpixels can include M+1 pixels, and the photosensitive detector caninclude N pixels, where N can be greater than M+1. The method can alsoinclude scanning the light beam over the target region in a pattern andrecording the positions of the detected light beam using a full number Nof detector pixels. The method can also include using the recordedpositions of the detected light beam to select the first and secondgroups of detector pixels. The method can also include summing pixels inthe first group of detector pixels prior to processing and summingpixels in the second group of detector pixels prior to processing. Themethod can also include summing pixels in the first group of detectorpixels after processing and summing pixels in the second group ofdetector pixels after processing. The method can also include using theselected first group of detector pixels to detect a position of thelight beam and selecting the second group of detector pixels when acenter of the detected position of the light beam is at a boundarybetween two pixels in the first group of detector pixels. The method canalso include scanning the light beam over the target region anddetermining an angle for each time the light beam crosses a boundarybetween two detector pixels using a full number N of detector pixels.The method can also include scanning the light beam over the targetregion and selecting a new group of M+1 detector pixels each time theangle of the light beam corresponds to one of the determined angles.

In an aspect, the disclosure can feature a system for dynamicallyadjusting a composite field of view in a lidar system. The system caninclude a transmitter configured to transmit a light beam towards atarget region at a first angle and then at a second angle. The systemcan also include a photodetector including a plurality of pixels. Thesystem can also include control circuitry configured to select a firstgroup of detector pixels to receive a portion of the light beam at thefirst angle and a second group of detector pixels to receive a portionof the light beam at the second angle from the target region. Thecontrol circuitry can be configured to subtract at least one detectorpixel from the first group of detector pixels and add at least onedetector pixel to the first group of detector pixels, such as to formthe second group of detector pixels. The received portion of the lightbeam can include an area corresponding to M detector pixels and thefirst group of detector pixels and the second group of detector pixelscan include M+1 detector pixels, and the photosensitive detector caninclude N detector pixels, where N can be greater than M+1. Thetransmitter can be configured to scan the light beam over the targetregion in a pattern and the system can include a memory, such as torecord the positions of the detected light beam using a full number N ofdetector pixels. The control circuitry can be configured to use therecorded positions of the detected light beam to select the first andsecond groups of detector pixels. The system can also include summingcircuitry that can sum pixels in the first group of detector pixelsprior to processing and can sum pixels in the second group of detectorpixels prior to processing. The system can also include summingcircuitry to sum pixels in the first group of detector pixels afterprocessing and sum pixels in the second group of detector pixels afterprocessing.

In an aspect, the disclosure can feature a method for dynamicallyadjusting a composite field of view in a lidar system. The method caninclude transmitting a light beam towards a target region. The methodcan also include receiving a responsive light beam from the targetregion onto a first group of pixels corresponding to a first compositefield of view. The method can also include adjusting an angle of thetransmitted light beam and, based on the adjusted angle of thetransmitted light beam, removing at least one pixel from the first groupof pixels and adding at least one pixel to the first group of pixels toform a second group of pixels corresponding to a second composite fieldof view. The method can also include then transmitting the light beamtowards the target region at the adjusted angle and receiving aresponsive light beam from the target region onto the second group ofpixels corresponding to the second field of view. The method can alsoinclude sequentially scanning a light beam across a target region anddetermining at least one angle of the light beam at which a receivedportion of the transmitted light beam is aligned with a boundary of atleast two pixels. The at least one angle of light beam can be determinedwhen a center of the received portion of the transmitted light beam isaligned with a boundary of at least two pixels.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 illustrates a diagram of a scanning lidar system.

FIG. 2 illustrates a diagram of a method for dynamically adjusting acomposite FOV.

FIG. 3 illustrates a diagram of a method for dynamically adjusting acomposite FONT.

FIG. 4 illustrates a diagram of an electrical system for dynamicallyadjusting a composite FOV.

FIG. 5 illustrates a method of operation of a scanning lidar system.

FIG. 6 illustrates a signal path in a scanned lidar system.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

FIG. 1 shows an example of portions of a lidar system 100. The lidarsystem 100 can include control circuitry 104, an illuminator 105, ascanning element 106, an optical system 116, a photosensitive detector120, and detection circuitry 124. The control circuitry 104 can beconnected to the illuminator 105, the scanning element 106 and thedetection circuitry 124. The photosensitive detector 120 can beconnected to the detection circuitry 124. During operation, the controlcircuitry 104 can provide instructions to the illuminator 105 and thescanning element 106, such as to cause the illuminator 105 to emit alight beam towards the scanning element 106 and to cause the scanningelement 106 to direct the light beam towards the target region 112. Inan example, the illuminator 105 can include a laser and the scanningelement can include a vector scanner, such as an electro-opticwaveguide. The electro-optic waveguide can adjust an angle of the lightbeam based on the received instructions from the control circuitry 104.The target region 112 can correspond to a field of view of the opticalsystem 116. The electro-optic waveguide can scan the light beam over thetarget region 112 in a series of scanned segments 114. The opticalsystem 116 can receive at least a portion of the light beam from thetarget region 112 and can image the scanned segments 114 onto thephotosensitive detector 120 (e.g., a CCD). The detection circuitry 124can receive and process the image of the scanned points from thephotosensitive detector 120, such as to form a frame. In an example, thecontrol circuitry 104 can select a region of interest that is a subsetof the field of view of the optical system and instruct theelectro-optic waveguide to scan over the region of interest. In anexample, the detection circuitry 124 can include circuitry fordigitizing the received image. In an example, the lidar system 100 canbe installed in an automobile, such as to facilitate an autonomousself-driving automobile. A field of view of the optical system 116 canbe associated with the photosensitive detector 120, such as in which theoptical system 116 images light onto the photosensitive detector 120.The photosensitive detector 120 can include and be divided into an arrayof detector pixels 121, and the optical system's field of view (FOV) canbe divided into an array of pixel FOVs 123 with each pixel FOSS' of theoptical system corresponding to a pixel of the photosensitive detector120.

In an example, one or more signals (e.g., measured charge or current)from a group of detector pixels 121 can be summed together, such as toform a composite FOV (e.g., a sum of detector pixel FOVs). The compositeFOV can be a subset of less than the full FOV. By changing which of thepixels are being summed together, the composite FOV can be adjusteddynamically. The summing can be done in various ways. For example, thesumming can be performed digitally, such as after some processing ofeach pixel in the active composite FOV. The summing can also beperformed by adding currents directly (e.g., by summing photocurrentsdirectly from the photodiode, or by converting photocurrents to avoltage, such as with a transimpedance amplifier and then summing thevoltages) from the photocurrent created by the light incident on thephotodetector. The summing can also be performed with a summingamplifier later in the signal path, such as the signal path 600 shown inFIG. 6 that can include a photodetector (PD) 610 providing a signal to atransimpedance amplifier (TLA) 620, the transimpedance amplifier 620providing a signal to a summation circuit 640 or second amplificationstage, followed by an analog-to-digital converter (ADC) 650. A first andsecond multiplexer 630 can process even and odd detector pixels of thephotosensitive detector, respectively. In an example where the detectorpixels can be consecutively numbered, even detector pixels can refer toeven numbered detector pixels and odd detector pixels can refer to oddnumbered detector pixels.

In an example in which an image of the object of interest (e.g., areflected or scattered portion of a light beam illuminating the targetregion) being detected can be smaller than the full FOV, reducing theFOV such as described herein can have numerous advantages. For example,by using a reduced. FOV for effectively reducing the active area of thephotodetector, noise, such as that introduced by one or more noisesources that scale with an area of the photodetector can be reduced.Examples of noise or other artifacts that can be reduced by reducing theactive area of the photodetector can include dark current in thephotodetector and gain peaking in an operational-amplifier circuit, suchas that caused by the capacitance of the photodetector. Additionally,the effect of background light can be reduced and any spurious lightsignals not present in the active composite FOV but present in the fullsystem FOV can be reduced, and in some examples, eliminated.

Alternatively, or additionally, the signal from an individual pixel canbe fully processed independently and then summing or one or more othertechniques can be performed in post-processing. This can have thedisadvantage of duplicating much of the full signal chain for eachindividual pixel (e.g., readout electronics for each individual pixelinstead of readout electronics for as few as one composite pixel). Thisduplication can occur in hardware (and thus can result in heatgeneration and power consumption and physical space) or additionally, insoftware and data-processing, and in many circumstances, may not befeasible.

A problem that may be associated with dividing the photodetector into asubset of smaller regions of the photodetector can be that a signal ofinterest can be present between the FOVs of two (or more) pixels. Insuch an example, the observed signal may be reduced when reading asingle pixel, because a substantial portion of the light can hitinactive pixels. By dynamically adjusting a composite FOV, this problemcan be reduced while still maintaining the benefits of having a reducedFOV. In an example, a technique for summing pixels can include varying acomposite FOV, such as to track a moving target (e.g., a light beamscanning over the target region) while fully capturing the light fromthe target. The composite FOV can be dynamically adjusted, such as basedon one or more of a location of the target, the size of the target, anda calibration of the FOV for each pixel. In an example, the compositeFOV can be automatically adjusted when the target spans a boundarybetween at least two pixels.

FIG. 2 illustrates a method for dynamically adjusting a composite FOV ina lidar system, such as the lidar system 100 shown in FIG. 1. In theillustrated method, which has been simplified to include a small number(e.g., less than 10) of detector pixels 121 merely for illustrativeclarity, the photosensitive detector can include five detector pixels121, the target 204 can have a dimension along the scanning direction oflarger than one detector pixel, but smaller than two detector pixels,and three detector pixels at a time can be summed to form a compositeFOV. The detector pixels being summed can be unshaded as illustrated inFIG. 2. In the illustrated method, the target (e.g., a reflected orscattered portion of a light beam illuminating the target region) canmove from left to right (from a low pixel index to a high pixel index),across the five detector pixels of the photosensitive detector as thelight beam scans across a target region. As the target moves from leftto right, the composite FOV can be dynamically adjusted, such as toprovide for capture of the entire target by the detector pixels formingthe composite FOV. In an example, the pixel having the lowest index canbe removed from the sum of detector pixels forming the composite FOV andthe next pixel in the target direction of motion (e.g., higher index)can be added to the sum of detector pixels forming the composite FOV,such as when the target is centered or otherwise spans two of thedetector pixels in the composite FOV. In an example, the photosensitivedetector can include N detector pixels, a size of a target can becaptured by m detector pixels, and a composite FOV can be formed bysumming m+1 detector pixels. In the example shown in FIG. 2, the targetcan move in a linear pattern, but the technique of dynamically adjustingthe composite FOV can be applied to an arbitrary pattern in one or twodimensions, so long as the arbitrary pattern can be determinable inadvance. Additionally, or alternatively, the technique of summing pixelsto form a composite FOV can be applied in one or two dimensions.

In a scanning lidar system, such as that shown in FIG. 1, the target canbe imaged by a light pulse emitted by the laser that can be reflected orscattered back from the target region to the receiving optical system.The target position can be determined based on an angle at which thelight pulse can be emitted from the laser, such as to determine apattern of the target based on the scan pattern of the laser.

In an example in which the target can be brighter than any backgroundsignals, such as in an active lidar system as shown in FIG. 1, or in afree-space optical communication system, the position of the target canbe determined from the corresponding signals collected by eachrespective detector pixel in the composite FOV. In an example in whichthe target image hits only two detector pixels, a difference in signalstrength of each individual detector pixel can be used to determine atarget position relative to the two pixels. By adjusting which pixelsare being summed and the corresponding composite FOV when the signalstrength is balanced or divided between two detector pixels, the pixelswitching can be handled automatically in real time.

In an example in which the target changes direction, the change indirection of the target can be detected based on the signal strengths ofeach pixel. In such an example in which the motion of the target can beslow compared with the update rate of the detector pixel signals, thelidar system can track the motion of the target. A position of thetarget can be determined by image processing either data from thephotosensitive detector or data from another sensor or a suite ofsensors, such as cameras, inertial measurement units (IMUs), or GPS.

FIG. 3 illustrates an example in which a size of the target beam can beless than a single detector pixel. In the example shown in FIG. 3, twodetector pixels at a time can be summed to form a composite FOV. In suchan example in which two adjacent detector pixels are summed to form acomposite FOV, FIG. 4 illustrates an example of an electronic system 400for performing the summing. The electronic system 400 can be included indetection circuitry, such as detection circuitry 124. In the exampleshown in FIG. 4, odd pixels can be electrically connected to the inputsof a first multiplexer 404 (MUX) and even pixels can be electricallyconnected to the inputs of a second multiplexer 408. The outputs of thefirst multiplexer 404 and the second multiplexer 408 can be connected toa summing amplifier 412, such as to sum any combination of adjacentpixels (e.g., pixel one and pixel two or pixel two and pixel three). Inan example in which N detector pixels at a time can be summed to form acomposite FOV, the detector pixels can respectively be connected to theinputs of N multiplexers, and the outputs of the respective multiplexerscan be summed to form a composite FOV.

In an example in which a composite FOV is less than a full FOV, thecomposite FOV can be matched to a dynamic area of interest. Matching thedynamic area of interest to the composite FOV can lower noise and makethe system less susceptible to spurious signals that are outside thecurrent composite FOV of the photodetector. For example, in a scannedlidar system, direct sunlight or other strong light sources may blind orsaturate a few detector pixels, but if these blinded or saturated pixelsaren't active detector pixels, then the system may not be blinded orsaturated by this signal. Increased noise from a non-blinding lightsource may also be avoided in an example in which the noise from thenon-blinding light source can be incident on inactive detector pixelsnot in the active composite FOV. In an example in which the compositeFOV includes a single detector pixel, a received signal may be reducedwhen the target moves outside of single pixel's FOV and is split betweenmultiple pixels.

FIG. 5 illustrates a method of operation of a scanning lidar system,such as the lidar system 100 shown in FIG. 1. A light beam can betransmitted towards a first target (step 510). A reflected or scatteredlight beam can then be received from the first target onto a first groupof pixels corresponding to a first composite field of view (step 520).An angle of the light beam transmitted from the laser can be adjustedand based on the adjusted angle of the transmitted light beam, at leastone pixel can be removed from the first group of pixels and at least onepixel can be added to the first group of pixels to form a second groupof pixels (step 530). The removing of at least one pixel and adding ofat least one pixel may be referred to as a pixel handoff. A light beamcan then be transmitted towards a second target and a reflected lightbeam can be received from the second target onto the second group ofpixels corresponding to a second field of view (step 540). A light beamcan be scanned across a target region and at least one angle can bedetermined based on where a received portion of the transmitted lightbeam can be aligned with a boundary of at least two pixels (steps 550and 560). In an example, a center of the received portion of thetransmitted light beam can be aligned with a boundary of at least twopixels.

In an example where pixel handoffs can be associated with an angle of alight beam transmitted by an illuminator, such as the illuminator 105shown in FIG. 1, the pixel handoffs can be used as calibrated anglemarkers, such as to provide an indication of changes in a beam steeringportion (e.g., scanning element 106) of a scanning lidar system. Thepixel handoffs can be used to provide recalibration of the beam steeringportion and can be used to compensate for drift in the beam steeringportion, such as due to aging, misalignment, mechanical impact,temperature drift, laser wavelength drift, or any other factor that canaffect the beam steerer. Although some of the examples herein have beendescribed in the context of a lidar system, the disclosure is equallyapplicable to passive receive systems such as free space opticalcommunication systems.

1. A method for dynamically adjusting a composite field of view in anoptical detection system having a photosensitive detector, the methodcomprising: selecting a first group of detector pixels for detecting aportion of a light beam transmitted towards a target region; adjustingan angle of the light beam transmitted towards the target region; andselecting a second group of detector pixels for detecting a portion ofthe light beam having the adjusted angle, the selecting the first groupof detector pixels and the selecting the second group of detector pixelsincluding using recorded positions of detected portions of the lightbeam.
 2. The method of claim 1, comprising subtracting at least onedetector pixel from the first group of detector pixels and adding atleast one detector pixel to the first group of detector pixels to formthe second group of detector pixels.
 3. The method according to claim 1,wherein the detected light beam has an area corresponding to M pixelsand the first group of detector pixels and the second group of detectorpixels include M+1 pixels, and the photosensitive detector includes Npixels, where N is greater than M+1.
 4. The method according to claim 1,comprising scanning the light beam over the target region in a patternand recording the positions of the detected light beam using a fullcount N of detector pixels.
 5. (canceled)
 6. The method according toclaim 1, comprising summing pixels in the first group of detector pixelsprior to digitization and summing pixels in the second group of detectorpixels prior to digitization.
 7. The method according to claim 1,comprising summing pixels in the first group of detector pixels afterdigitization and summing pixels in the second group of detector pixelsafter digitizations.
 8. The method according to claim 1, comprisingusing the selected first group of detector pixels to detect a positionof the light beam and selecting the second group of detector pixels whena center of the detected position of the light beam is at a boundarybetween two pixels.
 9. The method according to claim 1, comprisingscanning the light beam over the target region and determining an anglefor each time the light beam crosses a boundary between two detectorpixels using a full count N of detector pixels.
 10. The method accordingto claim 9, comprising scanning the light beam over the target regionand selecting a new group of M+1 detector pixels each time the angle ofthe light beam corresponds to one of the determined angles.
 11. A systemfor dynamically adjusting a composite field of view in an opticaldetection system, the system comprising: a transmitter configured totransmit a light beam towards a target region at a first angle and thenat a second angle; a photodetector including a plurality of pixels; andcontrol circuitry configured to select a first group of detector pixelsto receive a portion of the light beam corresponding to the first angleand a second group of detector pixels to receive a portion of the lightbeam corresponding to the second angle from the target region, theselecting the first group of detector pixels and the selecting thesecond group of detector pixels including using recorded positions ofreceived portions of the light beam.
 12. The system of claim 11, whereinthe control circuitry is configured to subtract at least one detectorpixel from the first group of detector pixels and add at least onedetector pixel to the first group of detector pixels to form the secondgroup of detector pixels.
 13. The system according to claim 11, whereinthe received portion of the light beam has an area corresponding to Mdetector pixels and the first group of detector pixels and the secondgroup of detector pixels include M+1 detector pixels, and thephotosensitive detector includes N detector pixels, where N is greaterthan M+1.
 14. The system according to claim 11, wherein the transmitteris configured to scan the light beam over the target region in a patternand the system includes a memory to record the positions of the detectedlight beam using a full count N of detector pixels.
 15. (canceled) 16.The system according to claim 11, comprising summing circuitry to sumpixels in the first group of detector pixels prior to digitization andconfigured to sum pixels in the second group of detector pixels prior todigitization.
 17. The system according to claim 11, comprising summingcircuitry to sum pixels in the first group of detector pixels afterdigitization and sum pixels in the second group of detector pixels afterdigitization.
 18. A method for dynamically adjusting a composite fieldof view in an optical detection system, the method comprising:transmitting a light beam towards a target region; receiving aresponsive light beam from the target region onto a first group ofpixels corresponding to a first composite field of view; adjusting anangle of the transmitted light beam and; based on the adjusted angle ofthe transmitted light beam, removing at least one pixel from the firstgroup of pixels and adding at least one pixel to the first group ofpixels to form a second group of pixels corresponding to a secondcomposite field of view, including using recorded positions of detectedportions of the light beam; and transmitting the light beam towards thetarget region at the adjusted angle and receiving a responsive lightbeam from the target region onto the second group of pixelscorresponding to the second field of view.
 19. The method of claim 18,further comprising: sequentially scanning a light beam across a targetregion; and determining at least one angle of the light beam at which areceived portion of the transmitted light beam is aligned with aboundary of at least two pixels.
 20. The method according to claim 18,wherein the at least one angle of light beam is determined when a centerof the received portion of the transmitted light beam is aligned with aboundary of at least two pixels.
 21. The method of claim 6, whereinsumming pixels in the first group of detector pixels prior todigitization comprises summing respective currents from the first groupof detector pixels; and wherein summing pixels in the second group ofdetector pixels prior to comprises summing respective currents from thesecond group of detector pixels.
 22. The system according to claim 11,wherein the summing circuitry is configured to sum respective currentsfrom the first group of detector pixels prior to digitization andconfigured to sum respective currents from the second group of detectorpixels prior to digitization.